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From: Davide Caratti <dcaratti@redhat.com>
To: Linux Kernel Network Developers <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next] net/sched: store the last executed chain also for clsact egress
Date: Fri, 30 Jul 2021 21:27:16 +0200	[thread overview]
Message-ID: <YQRSlETLgowgik2x@dcaratti.users.ipa.redhat.com> (raw)
In-Reply-To: <CAM_iQpU--x8PRprG8W6btdXFBr0bNnYaJF6CorELmK+tOgry=Q@mail.gmail.com>

hello Cong, thanks for looking at this!

On Wed, Jul 28, 2021 at 03:16:02PM -0700, Cong Wang wrote:
> On Wed, Jul 28, 2021 at 11:40 AM Davide Caratti <dcaratti@redhat.com> wrote:
> >
> > currently, only 'ingress' and 'clsact ingress' qdiscs store the tc 'chain
> > id' in the skb extension. However, userspace programs (like ovs) are able
> > to setup egress rules, and datapath gets confused in case it doesn't find
> > the 'chain id' for a packet that's "recirculated" by tc.
> > Change tcf_classify() to have the same semantic as tcf_classify_ingress()
> > so that a single function can be called in ingress / egress, using the tc
> > ingress / egress block respectively.
> 
> I wonder if there is any performance impact with this change? As
> tcf_classify() now may allocate skb ext (tc_skb_ext_alloc()) too,
> right after __tcf_classify().
> 
> Thanks.

I think there is some performance drop for users that activate
TC_SKB_EXT, in case packet doesn't match the filter *and* last
executed_chain is non-zero. But in this case, I also think it's a good
choice to spend some cycles to save the chain id in the extension: I
might be wrong, but AFAIK openvswitch is the only "user" that configures
TC in this way.

Do you have in mind a specific case where performance can be degraded
because of this commit? if so, I can try to investigate more.

thanks!
-- 
davide





  reply	other threads:[~2021-07-30 19:28 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 18:08 Davide Caratti
2021-07-28 21:41 ` mleitner
2021-07-28 22:16 ` Cong Wang
2021-07-30 19:27   ` Davide Caratti [this message]
2021-08-03  4:26     ` Cong Wang
2021-07-29 21:20 ` patchwork-bot+netdevbpf

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